Element and Compound. On the Scientific History of Two Fundamental Chemical Concepts

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thyroid gland [411. On the other hand, mothers having
demonstrable thyroid antibodies (Hashimoto’s thyroiditis) have children with chromosome anomalies,
especially children with a G-trisomy (Down’s syndrome), more commonly than healthy mothers. In
addition, patients with numerical or structural chromosome anomalies are more inclined to develop malignant tumors than the general population [421.
Chromosome aberrations can be caused in vitro in
primary normal fibroblast cultures if an extract of
genetically foreign lymphocytes is added. It has not
yet been made clear whether a classical immune mechanism is involved, or something else1431. Chromosome
changes also arise in normal tissue cultures after
activation of lysosomal enzymes (441; a tumor-inducing
factor could, for example, produce a breakdown of
lysosomes, whose released enzymes could cause chromosome breaks to recombine in a way that leads to the
formation of tumor cells.
We must assume that the majority of the possible morphological chromosome changes are not consistent
with cell life. Many findings indicate that immunological mechanisms can lead to chromosome changes.
For this reason it can be argued that such immune
reactions have a kind of self-protection function, in
which the “abnormal” cells are eliminated through an
alteration of the chromosome structure. A possible
defect in this self-protection system could be that not
all cells undergo lethal chromosomal damage and
some become so changed that, on the contrary, they
exhibit uncontrolled growth 141,451.
[41] For references see Ph. J . Fialkow, Blood 30, 388 (1967).
[42] R . W. Miller, New England J. Med. 87, 275 (1966).
[43] Ph. J . Fialkow and S . M . Gartler, Nature (London) 211, 713
(1966).
[44] A . C. Allison and G . R . Patron, Nature (London) 207, 1170
(1965).
[45] K . H . Bauer: Das Krebsproblem. Springer, Berlin 1963.
8. Outlook
Human chromosomes are very unsuitable for the investigation of many questions in genetics, especially
biochemical genetics, mainly because of their small
size. On the other hand, some of the difficulties could
be eliminated by greater cooperation in morphological, virological, and biochemical research. Thus, there
is a possibility of fractionating dividing cells and concentrating the chromosomes [461. The separation of
chromosomes or chromosome groups by physical
methods could yield further information on chromosome structure. An “in vitro system” of concentrated
chromosomes of defined morphology could reveal the
functional differences between individual chromosomes. On the cytogenetic side, experiments are already being undertaken to culture strains with defined
chromosome aberrations. Biochemical methods can
be used to try to find structural o r functional differences between these cells and normal cells, Already,
for example, a series of observations indicate that in
chronic myeloic leukemia the activity of the alkaline
leukocyte phosphatase is decreased, whereas in patients
with Down’s syndrome it is increased.
The goal of drawing up a gene map of the human chromosomes is still far in the future, and will probably
never be attained o n the same scale as in the case of
the giant chromosomes from the salivary gland of
Drosophila melanogaster, but it is not completely
hopeless; for instance, a large number of genes can
already be localized on the human X-chromosome,
and their sequence and approximate distance apart
can be determined.
Received: July 5, 1968
[A 654 IE]
German version: Angew. Chem. 80. 726 (1968)
Translated by Express Translation Service, London
[46] J. Mendelsohn, D . Moore, and N . Salzman, J. molecular.
Biol. 32, 101 (1968).
Element and Compound. On the Scientjfic History
of Two Fundamental Chemical Concepts[**]
BY E. STRoKERI*l
A wish is often expressed that any purely factual account be completed by a n historical dimension, where
not only a science’s past, like a venerable arsenal of the
factual knowledge possessed in earlier times, but also
the thought-structures which led to such knowledge in
the first place, should be called to memory. These
thought-structures, however, never belong exclusively
.
.. Seminar fur Philosophie der Technischen Universitat
(“1 Prof. Dr. Elisabeth Stroker
33 Braunschweig, Pockelsstrasse 1 4 (Germany)
[**I Based on a paper read at the general meeting of the
Cesellschaft Deutscher Chemiker, in Berlin (September 18-23, 1967).
718
to the past; they still find themselves as a precipitate in
contemporary scientific methods - a sediment in
present-day concepts.
In the following article we do not wish to
a
mere inventory of what was regarded at different
but rather to
times as element and as
examine a few, typical, clearly definable thoughtstructures, which have become what they now are
through the changing usage of the concepts of “element” and of “compound” in the course of the
history Of chemistry. The alchemistic doctrines of
Angew. Chem. internat. Edit.,’ Vol. 7 (1968)
1 No. 9
elements shall not be examined at all, and the concepts of “element” and “compound” will be considered only insofar as the history of their development has
been significant for chemical science.
*
These two concepts recall a very distant past. It is
commonly known that the earliest reflections on nature
are to be found in the Ionian philosophy of the Vth
century B.C. Just one hundred years later we find the
first “doctrine of elements”, which was to play a n
important role in chemistry right down to the Renaissance.
Fragments of a poem “On Nature” by the author of
this doctrine, Empedocles, a follower of the old
Pythagoreans, are still extant. I n his poem, Empedocles raises the question of the rhizomata, of the “roots”
of all things. He conceived them as four divinities
(that there should be four may be explained on the
basis of the Orphic-Pythagoric tradition, which regarded the number four as sacred): fire, earth, air, and
water. Empedocles supposes that all that exists is
composed of these. Things share in them in different
ways, and this is the reason why things are different.
Their composition may vary. Also the qualitative
changes, the coming-to-be and the passing-away of
things, are based on the mixture and exchange of such
particles. Each of the four “roots” is in itself unchangeable in mode and in quantity, and is not subject
to growth or decrease. It is likely that Empedocles also
conceived the idea of continuous exchange of fire,
water, earth, and air as an exchange of small particles,
imperceptible because of their smallness, so that all
obvious quantitative as well as qualitative changes are
ultimately based on the motion of such particles.
To be sure, the present-day chemist cannot expect to
do anything on the basis of this Empedoclean doctrine of elements, which is still tangibly captive of the
archaic-mythical Weltanschauung. But let us bring out
the posing of the question from which this doctrine
originated, in order to see how its significance went
far beyond just the material content of its own statements.
With the advent of Ionian natural philosophy a way of
thinking came into being, which would be of decisive
significance for the whole of Western science. Confronting the world, man asked of it as a whole - what
it was. He was not satisfied, however, with the mere
evidence of things and sought a deeper understanding
about what lasts as permanent behind their change,
about what their hypokeimenon- that which “underlies”
all coming-to-be and all passing away - may be. And it
was peculiar to this earliest philosophical thinking,
that it regarded no longer demons but material principles as being involved in the foundation of the world.
By assuming four such principles, which should explain the plurality and changeableness of sensible
phenomena, Empedocles establishes himself and his
doctrine within a much older tradition of thought.
He may be regarded, however, as the advocate of the
Angew. Chem. internnt. Edir. 1 VoI. 7 (1968) / No. 9
first doctrine of elements; the concept of the material
element originates from him. Though the designation
stoicheion was introduced later by Aristotle, the four
“roots” of all things, as Empedocles conceives them,
are already properly stoichaia, or elements
in the
specific sense, at least, and as understood not only by
the Greeks in their later classical doctrine of nature
but also by chemists up to the time of Robert Boyle.
This means that from the era of Empedocles on elements are basic materials, insofar as all material is
composed of them, i.~. all natural things originate
from them. The elements themselves, on the other
hand, are unoriginated, unchangeable, indestructible;
their total quantity in the universe must be regarded
as constant.
*
We shall not concern ourselves here with an examination of the reasons which later led to the peculiar
revision of this doctrine of elements by Leucippus and
Democritus. The most far-reaching aspect of their
philosophy of nature was that in it the qualitative difference of the elements was annulled, i.e. all material
qualities were reduced to purely mechanical processes
of motion of the corpuscles of a single matter. All
Democritean particles were of the same kind, distinguished from one another only in shapeand magnitude.
They were also thought to be unchangeable, unoriginated, imperishable, of finite magnitude, and yet
indivisible - atoma. The concept of atom was used
from then on to denote the smallest, reputedly (mechanically) indivisible particles of matter.
It has been necessary to briefly recall the Democritean
atomism, even though it not only failed to foster the
development of the previous doctrine of elements but
also actually did away with the very notion of element.
In so doing, however, this atomism was to be a constant and determining factor in the later discussion on
the nature of matter.
*
Democritus’ sharpest opponent, Aristotle, was the
successful continuator of this discussion but nowhere
in the history of chemistry does he find adequate appreciation; only the accusation of having fallen back
into the old doctrine of the four elements is leveled
against him. We are fully justified, then, in stressing
Aristotle’s role as author of a doctrine, which permanently influenced subsequent chemical thinking.
Problems of matter and of material change found their
honored place in the Aristotelian philosophy. The
first precise determination and elaboration of the
concept of matter - hyle - was done by Aristotle.
For Aristotle, however, matter is always qualitatively
determined matter. The assumption of a matter deprived of quality, whose atoma are merely differently
formed and only mechanically moved and ordered the Democritean corpuscular kinetic pattern of
change - is, according to Aristotle, wholly irreconcilable with that of experienced reality. Aristotle’s main
argument against Democritus presupposes quite def-
719
initely the acceptance of the tangible world. No aggregation of atoms but qualitative manifoldness and
fullness, not only mechanical motion but also development and change, coming-to-be and passing away this is what such a world exhibits.
Significantly, however, it is with this particular set of
problems that Aristotle runs into difficulties in his
criticism of Democritus. He was the first to see clearly
the distinction between a mixture and what was later
to be termed a chemical compound. The Greek word
mixis explicitly denotes a chemical compound as opposed to a mixture, for which the term synthesis is
used [I].
According to Aristotle, it is precisely here in the
interpretation of mixis - of the compound, therefore that atomism fails, since it does not succeed in explaining the amazing effect of henosis, of the “becoming
one” of different material elements in the entirely new
kind of matter of the mixis: for the qualities of a mixis
are not the summation of the peculiarities of the original materials but are wholly new and of a different
kind. Hence, Aristotle assumes that in the mixis the
original materials could not have remained unchanged,
even in their smallest particles, since otherwise the
compound would be nothing but a macroscopic illusion and actually only a mixture of the atoms of the
original materials.
Aristotle is well aware, on the other hand, that the
original substances which go into the making of a
compound - that is in the mixis - can be retrieved;
therefore, these substances can neither be lost nor
destroyed. The possibility of decomposing a compound into its component parts would seem to involve
precisely the opposite of what is suggested by the new
quality of the compound - no sooner is the problem
of the mixis seen and formulated with clarity, than it
leads to an aporia.
Briefly, Aristotle attempted to overcome this difficulty
as follows: it must be granted that in the mixis an
entirely new matter has arisen from the original materials; nevertheless, the components are present
dynamei, “potentially”, also in the compound. In the
compound the components are no longer what they
were as individuals; it is likely that they have undergone an intrinsic change. It is also true, however, that
the elements d o not perish in the compound, since it
is always possible to retrieve them by analysis of the
compound itself.
For the first time, some very significant questions are
raised, questions which have concerned chemists ever
since. It would no doubt be an error to regard Aristotle
as a chemist in order to easily dismiss him as an
amateur. The Aristotelian doctrine of mixis must be
regarded explicitly as a philosophical discussion of
principles. In other words, the doctrine must be considered here in its true context as an aim at clarifying
not chemical facts but rather those concepts without
which we would find it impossible to state with precision questions about such facts. The problem is not,
[l] Aristorle, De generatione et corruptione, 328a 1-13.
720
“what is matter and how is a mixis made from it”,
but, how is one to think of this mixis as existent tout
court.
*
On !he other hand, however, the question whether a
mixis can be understood as matter which “consists of”
other materials, is a later differentiation of the Aristotelian problem. Aristotle develops his discussion on
principles wholly within the framework of ordinary
language. In ordinary language, however, it is taken
for granted that a compound owes its existence to the
same materials of which it consists. (The present-day
chemist still says, for instance, that hydrochloric acid
“consists of” oxygen and chlorine, and finds this way
of expressing himself meaningful throughout.)
Aristotle established a way of questioning and reasoning, which was used in, and strongly influenced, discussions on the composition and structure of matter until
late in the XVIIth century. Such discussion was
carried on - though not without frequent interruptions
owing to the dominance of alchemy - in the main in
two clearly separate philosophical camps, without
first being related to chemical experience.
On the one hand, the old Democritean doctrine was
revived in the philosophy of the Stoics and found its
continuation in the so-called philosophical atomism.
According to its fundamental concept, however,
atomism could never have solved the Aristotelian
problem, viz.: how to interpret the formation of
chemical compounds from the elements and the possibility of analyzing the former into the latter. Atomism was even incapable of distinguishing between
these two categories of matter.
On the other hand, this distinction, clearly formulated
for the first time by Aristotle, became the cause of a
heated controversy in the Aristotelian camp on the
problem of the divisibility of matter. The appeal to
Democritus’ non-qualitative atoms of a single matter
did not at first contribute to its solution. There seemed
to be also a qualitative difference between the smallest
chemical particles of a given matter and those of
another. This assumption of the existence of the specific smallest particles of a given matter - of the
minima naturalia - played an important role throughout the Middle Ages, since it constituted the background on which was based the question of the nature
and the fate of the minima naturalia of the elements
when the latter form a mixis. In the minima naturalia
of the Aristotelian tradition we may easily recognize
the conceptual forerunners of the molecules of modernday chemistry. It is also easy to see how the distinction
between atom and molecule became possible only in
the realm of the doctrine of minima; it found no place
in ancient atomism.
*
Two reasons justify our turning our attention to Robert Boyle who, in the middle of the XVIIth century,
dealt thoroughly with the traditional doctrines of
elements and finally developed an entirely new conception of the chemical element. At last chemistry was
Angew. Chem. internat. Edit. 1 Vol. 7 (1968) No. 9
established as an empirical science. Further, in a remarkable attempt to derive a compromise between the
doctrines of atomism and of the minima naturalia,
Boyle was the first to successfully resolve the conflicting ideas surrounding the precise conceptual interpretation of the notion of a chemical compound.
Let us first consider this latter attempt of Boyles to
establish a compromise between the two doctrines an attempt which was based in part on important
preliminary work done by Sennert and Gassendi. On
the one hand, the atoms conceived by the atomists
were considered, at that time, to be too little “chemical”, in their qualitative indistinction, to be accepted
as ultimate building-stones of the material world. On
the other hand, the few basic principles of this doctrine
- magnitude, form, and motion - did prove their
usefulness in a mechanistic conception, which in the
physics of the time was scoring one success after the
other. From this standpoint one can understand
Boyle’s attempt to reduce once more all chemical
qualities to mechanical principles, and yet to take into
account that Democritus’ heaps of atoms apparently
were of no use to the chemist. For the elementary
materials, then, Boyle introduced the notion of texture - of an atomical pattern, as it were - to be determined exclusively on the basis of the geometrical and
topological properties of the smallest Democritean
particles. Chemical compounds could be explained
then as the coming together of several textures and
their re-organization into a structure through the
motion of particles - as the heterogeneous particles
taking part in the formation of a definite patternrzl.
This resulted in a doctrine that was a peculiar mixture
of atomism and that of minima naturalia. On the
one hand, it recognized the right of the doctrine of
minima naturaZia to stress the specificity of material
particles; on the other hand, it tried to explain this
specificity in terms of the corpuscles, and of their texture and structure. Though the explanation was mechanistic, it was able to overcome to a certain extent the
determined opposition which such explanation had
encountered up t o that time. The Democritean notion
of mere aggregates of corpuscles was superseded here
by the notion of structure - in place of the disordered
aggregate the organization of particles into structures
was now envisaged. The concept of structure, introduced by Boyle and so eminently important for chemistry, first silenced the centuries-old controversy on
the union of elements in chemical compounds.
*
Of n o lesser importance, however, was Boyle’s new
conception of a n elementr31. This notion, which different traditions had made obscure, is discussed by
Boyle for the first time within the framework of
empirical research. Experiments at last should decide
whether the materials which were hitherto considered
-~____
[2] The Works of the Honourable R. Boyle, 1772 (repr. Hildesheim, 1964-66), Vol. I, p. 493 f.; Vol. 111, pp. 17 f., 49 f.
[31 Ref. [Z], Vol. I, pp. 495f., 530f., 562.
Aiigew. Chern. internat. Edit.
1 Vol. 7 11968) No. 9
“elements” are indeed such and not actually compounds. As elements they had to exhibit themselves
as “perfectly homogeneous and simple”, not composed of other materials or of one another. And why
should there be only four elements? Indeed no reason
had yet been put forward which could have excluded
the possibility of a large number of elements.
The fundamental change in methodical outlook, which
Robert Boyle’s considerations brought about, can
only be fully appreciated, as it were, against the background of tradition. The older doctrines viewed
the elements only from the standpoint of their being
in all other materials, as basic materials; the question
of the existence of elements arose only in connection
with “compounds”. Boyle, on the contrary, asked
what sort of materials the elements were in themselves
and among other materials. By taking only chemical
simplicity into account and regarding it as the only
chemically essential determination, and further by
accepting the possibility of a large, still indeterminate
multiplicity of elements, Boyle opened up entirely new
fields of chemical research. He forcefully confronted
chemistry with its proper aim, viz.: to enquire into the
multiplicity of materials in order to differentiate between elements and compounds of such elements.
Boyle’s new concept of elements was bound to raise
questions, on whose answer alone would depend how
and in what sense other materials could be envisaged
as being composed of elements. It had to be experimentally established which of the materials could be
further analyzed, and whether, and if so how often,
this process could be repeated. These questions show
how stimulating Boyle’s ideas were for analytical
chemistry - it is not by chance that this name originated from him.
Can it be convincingly established, however, whether
a material is simple or compound? The chemist, apparently, would never be able to decide with absolute
certainty whether the products obtained by an analysis
are really the ultimately simple chemical materials or
whether new analytical methods would show that they
are still compounds.
Consequently, Boyle did not venture to actually
identify any materials as elements. The objection
voiced against him on this account fails to duly appreciate these considerations and overstates a rather
widespread interpretation of Boyle’s views on the
elements.
Boyle is often regarded as the author of the “analytical
definition” of elements. In such definition the notion
of element is explicitly determined in relation to the
status of the analytical methods used for its discovery.
The definition accordingly refuses to speak of elements “as such”. It is easy to see, however, that this
interpretation is anachronistic; it is also easy to see
how effortlessly it slipped into the history of science.
It is one thing to think of a chemical element as a
material which in itself is simple and cannot be further
analyzed chemically, but quite another thing to define
an element as a material which cannot be further
analyzed by experimental methods current at the time.
72 1
The statement that “there are chemical elements”
does not mean the same thing in both cases. In the
first case we are confronted with a metaphysical statement about a quality regarded as pertaining to the
material world. Boyle had this i n mind when he asserted that “nature makes use of elements”. Only in the
second case, however, where the existence of chemical
elements is tied to their experimental demonstrability,
does it correspond to an analytical definition. Boyle
did indeed clear the way for it, but it was Lavoisier
who first formulated it explicitly.
In the latter half of the XVIIIth century, a number of
epoch-making accomplishments in chemistry are connected with the name of Lavoisier. This seems to substantiate the opinion of those who identify Lavoisier
with the climax of a Copernican revolution in chemical thinking. He was responsible for the first systematic application and use of quantitative methods,
which led to the confutation of phlogistics and to the
grounding of the modern doctrine of oxidation.
Among other things, however, this brought about also
a decisive reform of the basic views on elements and
compounds - and this in a twofold way.
For one thing, the above-mentioned analytical definition of elements aquired significance. Seizing upon
Boyle’s insight that one could not be sure about the
elementary nature of any material if its chemical
analysis did not take place, Lavoisier gave it a methodically decisive interpretation, which constituted a
turning-point in chemistry’s scientific consciousness.
Lavoisier purged Boyle’s concept of element of all
metaphysical implications and directed this concept
exclusively on the expediency of the analytical experiment. Certain materials are chemically determined as
elements, insofar and so long as there is n o way of
further analyzing them. They are elements “pour nous,
ci notre igard”. The question whether nature itself has
produced elements as such lies beyond the ken of
chemical science 141.
If one is now to consider that for chemistry elements
are not only basic materials as a definite class of materials of which other materials are composed, but also
basic materials in a wider sense - that is, that the
notion of element as such is also the foundation of the
kind and structure of our knowledge of all remaining
materials - then it is clear that Lavoisier’s analytical
definition means much more than the prudent reserve
and self-criticism of its author would lead one to
believe. It was an expression of a state of things, whose
main significance could be grasped only by the later
theoretically advanced chemical science, viz.: that all
its statements could not refer ultimately to elements
as something simply given in nature but to fundamental hypotheses on the nature of the elements. Most of
these hypotheses have brilliantly stood the test of time.
The second result of Lavoisier’s reform - much more
tangible for positive research than the first - was his
[4] Oeuvres de Lavoisier, Paris (1862), Vol. I, p. 4.
722
interpretation of the processes of oxidation and of
reduction, which led to the objective determination of
several elements and compounds [51. Substances which
in earlier times were considered as chemically simple
as, for instance, water and calcareous metals, now
proved to be further decomposable compounds. And
conversely, materials which phlogistonists had held to
be compounds now had to be considered elements,
e.g., sulfur, phosphorus, hydrogen, oxygen, and
particularly the metals. What Lavoisier accomplished
with this transformation of views on elements and
compounds can be measured only in the light of chemistry’s later development - it was the start of an entirely new orientation of material systematics.
The first chemical terminology, developed in 1787 by
Lavoisier in association with G. de Morveau, Berthollet, and Fourcroy, was firmly constructed on the
principle of the new distinction between element and
compound. That this terminology has proved itself
useful up to the present day, if not in detail still in the
essentials of its systematics, is a clear sign of the level
of chemical knowledge attained through Lavoisier’s
work. It was the beginning of a chemical technical
language, of whose significance hardly anybody is
still aware, since it has long been taken for granted
that each science has its own technical terms.
At the same time, however, this terminology plainly
reflects the limits of XVIIIth century chemistry,
especially with regard to the element-compound
problem. It was not by chance that it went no further
than a terminology; all efforts to construct a symbolism, in fact, failed. It still lacked the theoretical foundation which was to be layed down for the first time
during the XIXth century. Through his quantitative
research on metal-ion precipitates, neutralization,
and metathesis, Richter, who was practically unknown
in his own day, managed for the first time to give the
concept of chemical equivalence a clearly defined
meaning and to lay down the foundations of stoichiometry. Lastly, Dalton’s atomic theory furnished the
basis for the clarification of Richter’s stoichiometric
results and for a first glimpse into the quantitative
composition of compounds. Dalton was the first to
recognize the significance of atomic weight in chemical
research. From then on the relative atomic weight
became the essential characteristic of an element [61.
Though the weights determined by Dalton have today
only an historical interest, his view must be regarded
as one of the most decisive turning points for XIXth
century chemistry. With it, in fact, not only was the
way open for a precise study of the chemical proportions for individual compounds, and thus for precise
quantitative knowledge on the structure of the material world and its laws, but Dalton’s insight also
served as a basis for the construction of a set of char11, pp. 225-233, 623-655.
[61 J . Dalton, A New System of Chemical Philosophy. London
1808; German translation by Fr. Wolfl, Berlin 1812, Vol. I, p. 237.
[ S ] Ref. [4], Vol.
Angew. Chem. internat. Edit.
1 VoI. 7 (1968) J No. 9
acteristic symbols, with few and very simple syntactical
rules for their application, so that one could speak of
a language of signs and formulas in the full meaning
of the term. Berzelius developed the symbolic language
further, and it was soon supplemented by structural
formulas. In its present form, this language is not only
a means of information but belongs so inalienably as
an essential methodical tool to modern chemistry, that
the latter would be simply unthinkable without it.
Furthermore, the elegance of this chemical signlanguage lies in its ability to illustrate the basic structure of chemical thinking in the simplest terms - the
basic distinction between element and compound;
any systematics with which the chemist attempts to
bestow order and clarity on the fullness and multiformity of the material world is finally oriented on
this distinction.
Thanks to Daltonian chemistry’s forceful stand on the
importance of atomic weight, a third important factor
comes into play in this connection. Far from simply
remaining a characteristic number for each element,
it served as a means of investigating the possibility of
relationships between different elements. This led in
the 1870’s to the drawing up of the periodic system of
elements, which constituted the basic structure for all
further systematization of matter. The atomic weight
- or better, the atomic mass - later lost its fundamental significance for this system and had to be replaced
by the nuclear charge of the atom. It still remains,
however, an historically essential fact that atomic
weight offered only one aspect - the most important
among several, however - to at least attempt to systematize the elements, a n ever greater number of which
was being discovered.
*
Timidly begun in 1817 with Dobereiner’s doctrine of
triads, carried on in the fifties about just as promisingly
by Pettenkofer and Dumas, half a century was to pass
before the periodic system of the elements was established. About 1865 Newlands spoke of a “law of octaves”, which he believed he had found in his drawing
up of the elements in horizontal series (according to
increasing atomic mass) and in vertical series (according to alleged chemical analogy of the elements) 171.
At the beginning this theory was regarded as something of a game and not taken very seriously. However,
the fundamental idea ofperiodicity, led later to Meyer’s
and Mendeleeff‘s periodic system of the elements - a
system that has proved of immense value for science
up to our own day [*I.
The historical details of this discovery, its testing and
verification, and lastly its subsequent completion and
correction ‘91 will not be dealt with here. The pertinent
question arises, however, what this system of the ele[7] J . A . R. Newlands, On the Discovery of the Periodic Law.
London 1884.
[S] L. Meyer, Die modernen Theorien der Chemie und ihre Bedeutung fur die chemische Mechanik. Breslau 1864; 5th Edit.
1884. D . MendeZeef, Die Grundlagen der Chemie. Petersburg
1869; German translation Petersburg 1891, p. 666f.
191 See E. Sfroker, Denkwege der Chemie. Freiburg-Munchen
1967, p. 189f.
Angew. Chem. internat. Edit. / Vol. 7 (1968) J No. 9
ments has meant for chemistry. For the present-day
chemist it may have long ago become a triviality; the
historian of science, however, may point out how
little this system can be taken for granted. For what
does it imply to say not only that chemistry has a
system, as indeed do some other sciences, but that this
system is (i) a system of the chemical elements, and
(ii) is determined by a periodic law?
That chemistry’s fundamental norm lies in a system of
elements is a statement of fact which for a long time
has been a banality for the present-day chemist. However, several centuries were required for this statement
of fact to attain clear scientific identity from the obscurity of a host of confused ideas. The final outcome
then, was that the chemist must understand the whole
of his object of research only in terms of an element or
as a combination of elements and nothing else, so that
to the chemist, the question of how a chemical substance is constituted is, therefore, equivalent to the
question about its composition of elements.
In order to illustrate the meaning of the periodicity of
this system, let us again refer to Boyle. It is difficult
for us to appreciate the magnitude of the result he
achieved and its effects on the history of science. By
breaking the chains of the old doctrine of the four
elements, Boyle confronted chemistry for the first time
with the possibility of an unlimited multiplicity of elements and with the prospect of a series of continued
discoveries of elements. Though the establishment of
the periodic system did not actually limit Boyle’s indeterminate multiplicity of elements, the latter was
strictly regulated according to the principles of the
system. The fact that up to that time every discovery
of an element had been more or less accidental or, at
any rate, could be directed by n o possible forecast,
caused also its chemical properties to appear more or
less arbitrary. Through its unequivocal place-disposition the periodic system therefore directed the searching and regulated the expectations of the finding of
new elements and their possibilities of forming compounds.
Its uniqueness consists precisely in the periodicity of
this system of elements. In the periodic recurrence of
a few basic properties, and in the regulated declension
of all other chemical and physical properties of the
elements, lies, in the final analysis, the normative and
real system-generating impulse of chemical science as
a whole. For although the periodicity of the system is
unable in principle to limit the number of elements,
it does in fact radically exclude the arbitrariness of unendingly “new” and forever “other” elements. It
seems to be an idle question to inquire whether chemistry could at all be possible as a science if it were not
based on a two-dimensional order of elements but only
on a one-dimensional series of “totally different” elements. At least it would not be so systematic as it
actually is.
*
On the threshold of the XXth century, chemistry could
afford less than ever to rest confidently on its own
laurels. New kinds of experiences not only urged it
723
beyond the already inquired but also compelled it to
radically revise its basic assumptions. The discovery
of radioactive elements that disintegrate spontaneously, and the discovery of cathode rays and of their
corpuscular nature posed peremptorily the problem
of the structure of the atom. The old notion of the unchangeability and indivisibility of the atom - and
with it of the elements - had finally died.
The gradual recognition of the mysterious language of
atomic spectra as a code on the subtler structure of
matter, culminating i n Bohr’s concept of atomic
structure in 1913, marked the beginning of a new era,
and of a new understanding of all that was contained
in the age-old question on the elements and their compounds. Modern atomic physics has given us the tools
for a deeper understanding of the hitherto enigmatic
order of the elements in the periodic system, and of
their existence and reactivity. “Atomic shell” “atomic
nucleus”, and electron “shell-structure”furnished the
first important concepts for the explanation of what
was traditionally called the “properties” and the
“qualities” of the elements. Finally, the Pauli principle
also provided a solution to the enigma of the periodic
law, which MendelCeff had already sought to resolve
by ever renewed and unsuccessful attempts. The
wonderful ground-plan of the periodic system could
now be reconstructed, and one could at last rationalize
the hitherto hidden order of the chemical elements.
*
Surely, also the chemically most important property
of the elements, viz.: the ability to enter into combination tout court, posed new and difficult theoretical
problems. Bohr’s theory of the atom still lacked the
adequate means to explain the mechanism of chemical
composition. It is well known that only with the help
of wave mechanics has it become possible to tackle
the theoretical problems which arose from the exten-
sive experimental work of molecular physics. Because
of the endless difficulties which stand in the way of a
complete wave-mechanical explanation of chemical
bonding for all possible molecules, it i s legitimate to
doubt whether one can speak strictly of a theory of
chemical bonding. Nevertheless, wave mechanics must
be regarded today as the basis of any explanation of
chemical bonding.
To be sure, the exemplary mathematical exactness of
this basis can blind n o one to the fact that with it the
world of matter has become for us something very
strange. Elements and compounds which, according
to a long-cherished view, the world still consists of,
could indeed be fully explained in the conditions of
their existence. But the natural scientist’s ageless
search for something permanent and unchangeable in
the material world cannot reach its goal. It has to
yield in our day to the knowledge of the essential
changeability, impermanence, and destructibility of the
old matter.
In conclusion, it should not be overlooked that this
knowledge has finally reconciled an ancient contradiction which lasted until modern times and whose earliest rudimentary expression can be seen in the Democritean-Aristotelian controversy. The latest developments of chemistry have carried it beyond the ancient
aporetic and have basically mediated the two positions.
Still based as mechanics on “atomistic” foundations,
it has dissociated itself nevertheless from the Democritean conception and is now to be thought of in
terms of structures and such structures are to be considered dynamically. The ancient quest of Aristotle
has thus been satisfied - his mixis, starting point of all
future problems regarding the concepts of “element”
and “compound”, can be interpreted without contradiction in present-day research.
Received: September 28, 1967
[A 655 IE]
German version: Angew. Chem. SO, 747 (1968)
Translated by Dr. A. Gervasi, Heidelberg
C 0M M UNI CAT10 N S
High-melting Aromatic Compounds as
Stationary Phases in Gas Chromatography
benzene with glass beads and evaporating the solvent under
an IR lamp 151. The rubrene cannot then be rubbed off the
carrier. The stationary phase consists of 1 wt-% of rubrene
By F. A . Holdinghausen, D . Freitag, W. Ried, and
I. Halasz 1*I
Dedicated to Professor K. Winnacker on the occasion of his
65th birthday.
t
z
ci2
c
0
When used as stationary phases[l.ZJ, solid organic substances combine advantages of gas-solid and distribution
chromatography. Whereas the organic compounds used
previously were not particularly stable to heat, our experiments were conductedwith high-melting aromatic compounds.
We built our own gas-chromatographic apparatus r3J. which
contained a flame ionization detector with an appropriate
rapid pen recorder and a flow-programming unit [41.
We obtained a stationary phase by mixing a solution of
rubrene (5,6,11.12-tetraphenylnaphthacene,m.p. -330 “ C )in
124
.-
Star!
1
)18151/
3
2
1
0
! lminl
Fig. 1. Separation of Cs- to Clynormal paraffins o n solid-coated glass
beads. Stationary phase: 1 %of rubrene on glass beads; 50 mg of rubrene
per meter of column. Internal diameter of colum-n 2.3 mm; sieve fraction
0.10-0.12 mm. Carrier gas Nz. A p = 3.0 atm; JJ = 20cmisec. Quantity
of sample 5 ug. Ordinate: ionic current of the flame ionization detector.
Angew. Chem. internat. Edit. 1 Vol. 7 (1968)
/ No. 9